In an SmFe-based magnetostrictive material, it is necessary to finely divide or atomize the crystal grains of the SmFe-based magnetostrictive material in order to enhance the magnetostrictive performance in a lower magnetic field and to enhance the mechanical strength. The means that has been conventionally employed to accomplish this involves carrying out a casting operation of the material using a casting mold of copper having a larger thermal capacity to quench and solidify the molten metal. However, this conventional casting means is accompanied by a disadvantage that smaller and larger-sized grains of the SmFe-based magnetostrictive material are liable to be irregularly mixed together, because the size of the crystal grains is governed by the shape, the thermal capacity and the like of the casting mold of copper, and the specific heat, the vapor pressure and the like of the SmFe-based magnetostrictive material.